I had submitted Sitemap to Google and it was showing 404 error and when after number of days diagnosed the problem with Wordpress Plugin which was not generating XML file.... I would like to know of a Plugin which can generate Sitemap on Demand like used a Sitemap Plugin long ago which will rebuild the entire Sitemap from Wordpress Dashboard and notify Google of changes.... Suggestions required from people of such a Plugin...
I use https://wordpress.org/plugins/google-sitemap-generator/ it works perfectly. If you'll still have a 404 problem in your WM tools then you should manually check it (sitemap) if those pages are really exist